Process for recovering selenium and noble metals from electrolytic slimes and the like



RTE D. STATES PAET MASUIMI GmASHIG-E AND DENZO UN'O, OF KYOTO, JAPAN.

PROCESS FOR REGOVEAING SELENIUM AN'D NOBLE METALS FROM ELECTROLYTICSLIMES AND THE LIKE.

No Drawing.

Kamikyo-ku', Kyoto, Japan, both J apanese' subjects, have inventedcertain new and useful'Improvements in and Relating to a Process forRecovering Selenium and Noble Metals from Electrolytic Slimes and thelike; and we do hereby declare the following to be a full, clear, andexact description of the invention, such as will enable others skilledin the art to which it appertains to make and use the same.

This invention relates to a process for extracting non-metallic elementsof the sulphur grou and the noble metals, such as silver, gol platinumand the like, from refuses, for example, electrolytic slimes, mattes andfluedust, produced in refining copper, silver, gold platinum and similarmetals.

This invention consists in completely separating-selenium and otherelements of the sulphur group and the noble metals from each other, andin bringing elements in both groups by the same operation into suchforms as render them readily recoverable. Separating the two groups andat the same time bringing thehelements in both groups into easilyrecoverable form has, so far as we know, been impossible in any knownprocess heretofore used.

The process consists in fusing a mixture containing the non-metallicelements of the sulphur group and the noble metals with reagents capableof effecting a separation of these constituents from each other, infusion products of different specific gravities insoluble in each other,andrecovering from the fusion-products the valuable contents. This may'beattained by fusionwith a collector of the noble metals, preferablylead, and an alkali metal compound: Suitablealkali metal compounds arethe caustic alka-- lies and the alkali carbonates and nitratesa Alkalimetal compounds of this character are generically designated by theexpression an alkali metal flux. When the fusion is completed the massnaturally divides itself into three layers or zones according to thedifference of specific gravities of its constituents. All the noblemetals contained in Specification of Letters Patent.

recover both at the same time. to this invention it is possible torecover the Patented May 9, 1922.

Application filed October 1, 1919. Serial No. 327,736.

the material, will constitute-the bottomlayer in the form of a leadalloy or alloys while selenium and the like, forming compounds with thealkali-metals, will float and form the uppermost layer. The remainingmetals together with other metallic salts will constitute the middlelayer.

The object of this invention is to provide a very simple, efficientand-inexpensive process whereb all the selenium and other elements of te sulphur group and the noble metals contained in the materials treated,

may be extracted and completely recovered in elemental form.

If selenium or other elements of the sulphur group are contained'even ina tracein any noble metal, the good 'quality of such metal is damaged'The removal of such impurity during refining is, therefore, a matter ofgreat importance.

Since selenium and like elements have strong chemical ailinity for thenoble metals, and as they appearin the same group with the latter incourse'of analysis, it has hitherto been practically impossible toseparate the non-metallic elements and the noble metals one from theother, in such a manner as to According non-metallic elements of thesulphur group and the noble metals from a mixture containing the samewithout substantial loss of any of the constituents. This is realized byutilizing the following properties in combination, namely, (1) prominentchemical af- .finitybetween non-metallic elements of sulphur group andalkali-metals, (2) easy formation of alloys of lead with noble metals, I

and natural separation of non-metallic elements of sulphur groupcombined with alkali-metals, on the one hand, and alloys of lead withnoble metals, on the other, accord ing to thedifi'erence of specificgravities of the products in the fused state.

. In order that the invention may be ea sily v understood, anapplication of the process for extracting and recovering the elementselenium and the noble metals from an electrolytic slime produced incopper refining, will now be described and illustrated, by way ofexample.

In carrying out the process for example, with electrolytic slime whichusuall contains selenium, silver and gold as wel as a small proportionof copper, one or more of the caustic alkalies, alkali carbonates ornitrates, is added to the slime in such quantity as is sufficient, ormore than sufiicient to convert the whole of the selenium contained inthe slime into alkali compounds of selenium. .At the same time, lead isalso added to the slime in such av proportion as to form an alloy withthe noble metal contained therein. If lead is present in the slime used,the addition of the same may be entirely omitted or the amount decreasedin proportion to the lead-contents of the slime, The ingredients arecarefully mixed and subjected for two or three hours to a suitabletemperature, preferably 800-900 0., which will vary according to theamount of selenium and alkalies present. It is understood that thetemperature and time factors will vary somewhat with the character ofthe material under treatment. lVhen the chemical reaction is completed,the fused substances naturally separate into three layers according tothe difference of specific gravities of the respective fusion-products.

The noble metals converted into lead al-" loys will form the undermostor bottom layer together with a portion of copper if the same is presentin the original material treated.

The alkali selenides, selenites or selenates will form the uppermost orsurface layer, while the middle layer will be composed of residualcopper and other metallic salts in case copper or other metals arecontained in the material originally treated.

Chemical reactions occuring during the fusion, may be represented by thefollowing equation where, for brevity, it is assumed that the noblemetal present is silver only 1. When caustic soda is used:

2. Then sodium carbonate is used 3. When sodium nitrate is used:

It is understood that similar reactions will occur if gold, platinum orother metals of this group are present in the material undergoingtreatment.

The function of the lead is simply to form alloys with the noble metalswhich are present in the free state during fusion.

The separation of gold and other noble metals may be accomplished by anywell known process for example, cupellation.

In order to recover the selenium from the surface layer-mass the latteris dissolved in water and an acid, for example, sulphuric orhydrochloric, added thereto to neutralize the excess alkali, after whichair is passed through the solution to precipitate the selenium present.This-reaction may be represented by the following equation Selenium maystill remain as selenite or selenate in the solution. It may be reducedto elementary form by passing sulphur-dioxide .through the acidifiedsolution, and this reaction may be represented by the following equationNa,SeO,+2SO +H O:Se-l-2NaHSO,

Tellurium may often occur associated withselenium in the slime and ifpresent passes into the surface layer together with selenium and othernon-metallic elements.

When the surface layer is treated in the manner stated above, telluriumis precipitated at the same time as selenium. Separation of telluriumand selenium may be effected by any of the known processes.

The process of this invention may be applied to mattes and flue dust inexactly the same manner as in the case of eletrolytic slimes except thatthe mattes must be finely pulverized before alkalies are added to thesame.

We claim 1. A process for treating material containing non-metallicelements of the sulphur group and the noble metals, compris-.

ing fusing the same in the presence of a collector of the noble metalsand an alkali metal flux, and recovering the non-metallic elements ofthe sulphur group and the noble metals from the fusion-products.

2. A process for treating material containing non-metallic elements ofthe sulphur group and the noble metals, comprising fusing the same inthe presence of lead and an alkali metal flux and recovering thenonmetallic elements of the sulphur group and the noble metals from thefusion-products.

3. A process for treating material containing non-metallic elements ofthe sulphur group and the noble metals, comprising fusing the same inthe presence of lead anda sodium flux, and recovering the nonmetallicelements of the sulphur group and the noblemetals from thefusionsproducts.

Lamaze 4. A process 'for treating material containing selenium and thenoble metals, com prising fusing the same in the presence of a collectorof the noble metals and an alkali 5 metal flux and recovering theselenium and the noble metals from the fusion-products.

5. A process for treating material containing selenium and the noblemetals, comprising fusing the same in the presence of lead and an alkalimetal flux, and recover- 10 ing the selenium and the noble metals fromthe fusion-products.

In testimony whereof, we afiix our signatures.

MASUMI GHIKASHIGE.

DENZO UNO.

